Method for sensitizing compositions to radio frequency energy

ABSTRACT

A composition of enhanced radio frequency sensitivity and a method for providing enhanced radio frequency sensitivity to a composition in which a substance suitable for enhancement of radio frequency sensitivity is admixed with a radio frequency sensitizing amount of an inorganic radio frequency sensitizer treated essentially to remove absorbed water and/or other volatiles with the radio frequency sensitizer chosen from among zinc oxide (American Process), bentonite clay, and crystalline or amorphous alkali or alkaline earth metal aluminosilicate. A process for molding using these compositions and the molded product. The composition, method for enhancing radio frequency sensitivity, process for molding and molded product with a polymeric substance, particularly ultra high molecular weight polyethylene, as the substance suitable for enhancement of radio frequency sensitivity.

This application is a divisional application of application Ser. No.707,613 filed on Mar. 04, 1985, now U.S. Pat. No. 4,661,299.

BACKGROUND OF THE INVENTION

This invention relates to the enhancement of sensitivity of compositionsto radio frequency energy. In one of its aspects it relates tocompositions that are transparent to radio frequency energy. In anotherof its aspects this invention relates to compositions that have lowsensitivity to radio frequency energy. In another of its aspects thisinvention relates to compositions whose sensitivity to radio frequencyenergy has been enhanced.

It is known that sold hygroscopic fillers can be added to certainpolymer compositions to provide receptivity to microwave (MW) radiation(See U.S. Pat. No. 4,234,636). It has been noted that the microwavereceptivity of these polymer compositions is significantly reduced bydrying the fillers before compounding with the polymers. It has,therefore, been suggested that water associated with the hygroscopicfiller is responsible for the MW receptivity.

It is also known that polar organic compounds can be admixed withparticulate inorganic materials such as silicas to provide MWsensitizing compositions suitable for blending with polymers to provideMW receptivity to the resulting polymer compositions (See U.S. Pat. No.4,360,607).

It has now been found that certain inorganic compounds can provide radiofrequency (RF) radiation receptivity to a wide variety of compositions,especially polymers, after these inorganic compounds have beenessentially dried and in the absence of added polar organic compounds.This invention, therefore, provides many opportunities to utilize RFradiation for heating of compositions containing these certain inorganiccompounds so that a multiplicity of products, such as molded objects,can be produced for a multiplicity of purposes.

It is, therefore, an object of this invention to provide a method forenhancing the radio frequency sensitivity of compounds to which theprocess is applicable. It is another object of this invention to providecompositions of enhanced radio frequency sensitivity. It is stillanother object of this invention to provide compositions containingcertain inorganic compounds so that these compositions have enhancedradio frequency sensitivity as compared to the compositions withoutthese inorganic compounds. It is still another object of this inventionto produce molded objects by subjecting compositions of enhanced radiofrequency sensitivity to radio frequency energy in a molding operationsuch as transfer, injection or compression molding. It is still anotherobject of this invention to enhance the radio frequency sensitivity ofsuitable polymeric materials, particularly ultra high molecular weightpolyethylene.

Other aspects, objects and the various advantages of this invention willbecome apparent upon reading this specification and the appended claims.

STATEMENT OF THE INVENTION

In accordance with this invention there are provided compositions inwhich there is a substance suitable for enhancement of radio frequencysensitivity and a radio frequency sensitizing amount of an inorganicradio frequency sensitizer treated essentially to remove absorbed waterand/or other volatiles said sensitizer chosen from the group consistingof (1) zinc oxide (American Process), (2) bentonite clay, and (3)crystalline or amorphous alkali or alkaline earth metal aluminosilicate.

In an embodiment of the invention a method is provided for enhancing theradio frequency sensitivity of a substance suitable for such enhancementin which there is admixed with the substance suitable for radiofrequency enhancement a radio frequency sensitizing amount of aninorganic radio frequency sensitizer treated essentially to removeabsorbed water and/or other volatiles with a sensitizer chosen from thegroup consisting of (1) zinc oxide (American Process), (2) bentoniteclay, and (3) crystalline or amorphous alkali or alkaline earth metalaluminosilicate.

In another embodiment of the invention compositions in accordance withthe radio frequency enhancement of this invention are subjected to radiofrequency energy in a process for producing molded objects.

The suitable inorganic RF sensitizers employed in the instant inventionare selected from the group consisting of: zinc oxide (AmericanProcess), bentonite clay, and crystalline or amorphous alkali oralkaline earth metal aluminosilicates.

"American process" zinc oxide is a well known commercially availablematerial. As distinguished from the "French process" material, the"American process" zinc oxide is obtained by roasting of a suitable zincore whereas the "French process" employs an oxidation of vaporized zincmetal. An example of a suitable zinc oxide is AZO-55 from AmericanSmelting and Refining Co. Columbus, Ohio with typical properties asshown below:

    ______________________________________                                        TECHNICAL VALUES (Average)                                                    ______________________________________                                        Physical Properties                                                           Specific Gravity     5.6                                                      One Pound Bulks Gallons                                                                            0.0214                                                   Apparent Density (Lbs./cu. ft.)                                                                    32                                                       Particle Diameter (Microns)                                                                        0.27                                                     Surface Area (Sq. m./gm.)                                                                          4.00                                                     Rub-out Oil Absorption                                                                             14                                                       Fineness thru 325 Mesh (%)                                                                         99.95                                                    Chemical Analysis                                                             Zinc Oxide (ZnO)     99.20%                                                   Lead (Pb)            0.02%                                                    Cadmium (Cd)         0.05%                                                    Sulfur (S)           0.03%                                                    H.sub.2 O Soluble Salts                                                                            0.30%                                                    Insoluble in HCl     0.15%                                                    Loss at 105° C.                                                                             0.10%                                                    ______________________________________                                    

Bentonite clay, particularly the "Western type", is disclosed in U.S.Pat. No. 4,234,636 as a hygroscopic filler in the prior art processnoted. However, bentonite clay, especially the Western type, is alsosuitable in the instant invention after a heating step to drive offadsorbed water. Bentonite clay is a naturally occurring materialcontaining appreciable amounts of the clay mineral montmorillonite, (Mg,Ca)O.Al₂ O₃.5SiO₂.nH₂ O. As noted above bentonite clay obtained from theWestern states of the USA is preferred for use in the instant invention.A particularly useful Western bentonite material is Nygel-5 fromIndustrial Minerals Ventures, Inc. Lathrop Wells, Nev.

The alkali or alkaline earth metal aluminosilicates are a preferredgroup of RF sensitizers according to this invention. These materials canbe either amorphous or crystalline in nature and can be obtained bysynthetic methods. The alkali metal ion can be lithium, sodium, orpotassium preferably sodium, while the alkaline earth metal ion can bemmagnesium or calcium, usually calcium. It is also possible forcombinations of the above ions to be present in the aluminosilicatessuch as sodium and calcium. Suitable amorphous aluminosilicates areexemplified by the commercially available Zeolex 23, Zeolex 7-UD, orZeolex 7A from J. M. Huber Corp. Havre de Grace, MD. The suitablecrystalline aluminosilicates encompass the well known crystallinezeolites which are crystalline compounds composed of tetrahedrons ofsilicon oxide in which aluminum atoms have replaced some of the silicon.The zeolites are well known for their ion exchange behavior andmolecular sieve character. Suitable synthetic crystalline zeolitesinclude those within the families of Type A, Type D, Type L, Type R,Type S, Type T, Type X, Type Y and Type ZSM-5. More specific examplesinclude Types 3A, 4A, 5A, 10X, 13X, ZSM-8 and ZSM-11.

The average particle size (diameter) of the inorganic RF sensitizers ofthis invention is generally within the range of about 0.25 micron toabout 15 microns, preferably from about 0.5 micron to about 7 microns.The surface area (BET method) can range from about 1 m² /g to about1,000 m² /g, preferably from about 200 m² /g to about 500 m² /g. Forbest results, if a material with low surface area is chosen the particlesize should be as small as practicable. Conversely, if a material oflarge particle size is chosen the surface area should be as high aspracticable. In some instances it may be desirable to subject thematerial to a preliminary size reduction step to improve itseffectiveness as an RF sensitizer in the application underconsideration. This also may be especially helpful when the RFsensitizers of this invention are intended for use in polymercompositions. It is generally true that the physical properties ofpolymer are least affected when the particle size of the added materialis at the smallest end of the range. Size reduction can be accomplishedby conventional methods such as grinding, ball milling and the like.

As noted above the inorganic RF sensitizers of the instant invention aresubjected to a preliminary treated step which effectively removesadsorbed water and/or other volatiles which might be present. Theconditions employed in the treated step can vary widely depending on theamount of adsorbed water and/or other volatiles present among otherconsiderations. Usually heating to a constant weight will be adequate toprovide an inorganic RF sensitizer of this invention free of adsorbedwater and/or other volatiles. Generally, the temperature can range fromabout 100° C. to about 300° C. while the time can range from about 0.5hour to about 72 hours in the heating step of this invention. Theheating can be carried out at atmospheric pressure and in a flowing gassuch as air, nitrogen, argon or helium if desired. The heating also canbe conducted under reduced pressure such as achieved by conventionalvacuum pumps.

The inorganic RF sensitizers of this invention which have been treatedas described above can be mixed with the material to be subjected to RFradiation in a variety of conventional methods.

For polymer compositions it is particularly effective and preferred todry blend the inorganic RF sensitizer with solid polymer particles whichmay contain other conventional additives such as antioxidants, pigments,fillers and the like. The polymer particles will preferably have anaverage particle size of from about 10 mesh to about 40 mesh thoughsmaller or larger particles can be employed if desired. It is alsopossible to use a melt blending operation to incorporate the inorganicRF sensitizer into a polymer composition such as by employing a mixingextruder. The RF sensitizer can be added before, after, or duringaddition of other polymer additives in the mixing extruder operation.

It is also possible to prepare a dispersion of a finely dividedinorganic RF sensitizer in a liquid which is essentially inert to RFradiation e.g. alkanes having 5-30 carbon atoms, and then contacting thematerialto be made RF sensitive with said dispersiion as by spraying,milling, tumbling or stirring without or with subsequent removal of thedispersiion vehicle such as by vacuum assisted evaporation.

For RF transparent polymers the amount of inorganic RF sensitizeremployed according to this invention can be broadly from about 1 wt. %to about 20 wt. % based on the weight of the total composition.Preferably, the amount will range from about 4 wt. % to about 6 wt. % onthe same basis as above. These ranges are also particularly suited to RFequipment of about 1 kW power at 100 MHz frequency. For RF equipment ofhigher power and frequency it would be expected that the amounts of RFsensitizer can be reduced.

Furthermore, if the polymer employed has some RF responsiveness then theamount of RF sensitizer can also be reduced since the RF absorptioneffects of polymer and sensitizer are additive.

In the USA the Federal Communications Commission (FCC) has designatedcertain radio frequency bands centered about 50 MHz, 915 MHz, 2450 MHz,5800 MHz and 22000 MHz for industrial heating units to minimize conflictwith communication systems. The compositions which are RF sensitizedaccording to the instant invention can be treated with electromagneticradiation of preferably from about 1 MHz to about 2500 MHz, morepreferably from about 20 MHz to about 1000 MHz.

Several manufacturers provide equipment suitable for generating the RFradiation within the needed ranges. An example is Thermall #9 ElectronicHeatingEquipment with 1.25 kW power at 100 MHz made by W. T. LaRose &Associates Troy, NY.

Power absorption is governed by the equation P=1.41 (E/D)² ×f×E" where Pis in watt/in³, E is the electrode voltage in kV, D is the electrodedistance in inches, f is frequency in MHz and E" is the dielectric lossfactor which is the productof the dielectric constant, E', anddissipation factor, tan Δ. This equation is well known to those skilledin the art of RF or MW heating and can be used to adjust availableequipment to the compositions being treated with RF energy.

Broadly speaking, the inorganic RF sensitizers of the instant inventionare useful in essentially any composition wherein the inorganic compoundis not materially detrimental and which is to be subjected to RFradiation for heating purposes. Thus, the inorganic RF sensitizers ofthis invention provide opportunities to use RF radiation for heating ina multitude of application.

One area of application that is especially important involves polymerprocessing. In operations such as injection molding, transfer molding,blow molding, vacuum forming, extrusion, softening, foaming, shaping,curing and the like the RF sensitized polymer compositions can besubjected to RF radiation to efficiently provide the needed heat toaccomplish the desired operation. The inorganic RF sensitizers can beused in presence of other polymer compounding ingredients such as carbonblack which are also RF sensitive to some extent to enhance the level ofRF sensitivity of the composition. This enhancement can also be obtainedwith the use of the inventive inorganic RF sensitizers in certain polarpolymers which are in themselves RF sensitive. One particular areawithin the field of polymer processing that is especially aided by theinorganic RF sensitizers of this invention is that of handling ultrahigh molecular weight polyethylene (UHMWPE). It is reciognized that thismaterial has many desirable properties but the ultra high molecularweight which is apparently responsible for the desirable properties alsomakes this material extremely difficult to process. RF heating has beenutilized with carbon black as the RF sensitizer but this has not beenentirely satisfactory especially if articles having color other thanblack are desired. According to the instant invention the UHMWPEmaterial can be intensively mixed with an inorganic RF sensitizer ofthis invention and then subjected to RF radiation during the molding,e.g. transfer, injection, or compression molding, of various articlestherefrom.

The following are processes and composition suitable in processesillustrative of the present invention. These examples should be taken asillustrative and should not be considered to be restrictive.

EXAMPLE I

A large number of inorganic powders was tested for RF responsivenessbefore and after drying (heating) at 138° C. (280° F.) for 18 hours. Thetests were conducted by placing a weighed portion of the inorganicpowder in a Teflon dish sample holder of 3 3/32 inch cavity diameter and1/2 inch deep which could be covered with a 1/4 inch thick Teflon lid.The sample holder was placed between 6 inch×6 inch electrode platens set11/2 inches apart in a Thermall #9, 1.25 kW, 100 MHz heater made by W.T. LaRose and Associates Troy, NY. Each sample was exposed to the RFradiation for the indicated time while the current flow in milliamperes(mA) and temperature reached (°F.) by the sample were noted. Thebackground or "no-load" current reading was 167 mA. Temperaturemeasurement was obtained with a needle pyrometer inserted into thesample at several points and the highest reading recorded. Temperaturesgreater than about 600° F. were estimated. Table Ia presents resultsobtained for a number of inorganic powders which after drying were ratedas "nonresponsive" to "fair" response. Table Ib presents results forcertain amine treated or silane treated clays which were rated as having"moderate" response after drying. It should be noted that the claytreating agents such as amino compounds would be expected to addpolarity to the clays and thus provide some degree of RF sensitivity.The materials in Tables Ia and Ib are thus outside the scope of theinstnt invention. Table Ic presents results on inorganic powders whichafter drying show "Good" to "Excellent" RF response and these illustratethe RF sensitizers of the instant invention.

It is surprising that the American process zinc oxide was "very good" inRF response (Table Ic) after drying while the French process zinc oxideis essentially "nonresponsive" even before drying. In addition, it issurprising that the other materials in Table Ic were "good" to"excellent" in RF response after drying.

                                      TABLE Ia                                    __________________________________________________________________________    Example I                                                                     Results of RF-Response of Various Inorganic Powders                           None-Fair Response                                                                            Amount                                                                             Exposure,                                                                           Not Dried                                                                             Dried                                      Material        Grams                                                                              Seconds                                                                             mA   °F.                                                                       mA  °F.                                                                       Observations                        __________________________________________________________________________    Precipitated Hydrated Silicas                                                 Hi Sil 233 (PPG)                                                                              25   30    50-30                                                                              250                                                                              2-7 185                                                                              Condens.sup.a both cases            Silene D (PPG)  15   30    35-46                                                                              275                                                                               5-10                                                                             231                                                                              Condens.sup.a both cases            Sipernat 22 (Degussa)                                                                         17   30    35-34                                                                              262                                                                               2-12                                                                             215                                                                              Condens.sup.a both cases            Other Silicas                                                                 Syloid 74 Silica gel                                                                          25   30    15-12                                                                              165                                                                               8-11                                                                             196                                    (Davison)                                                                     Syloid 308, hydrophobized                                                                     25   30    20-15                                                                              183                                                                              0-6 148                                    silica gel                                                                    Imsil A-108 (Ind. Min. Sil)                                                                   25   30    10-13                                                                              147                                                                              3-7 130                                    Carbonates                                                                    Altowhite UF, CaCO.sub.3                                                                      25   30    0-6  105                                                                              0-3 130                                    (Georgia Marble)                                                              Magcarb L, MgCO.sub.3 (C. P. Hall)                                                            12.5 30    145-65                                                                             360                                                                              25-47                                                                             380                                                                              Fair Response                       ZnCO.sub.3      25   30    180-45                                                                             345                                                                              0-6 180                                    Talc, Mica                                                                    Emtal 549 (C. P. Hall)                                                                        25   30    2-8  115                                                                              0-3 155                                    Mica P-12 (C. P. Hall)                                                                        25   30    40-32                                                                              280                                                                              11-22                                                                             150                                    Calcined Clays                                                                Polyfil 70 (J. M. Huber)                                                                      25   30    0-7  120                                                                              0-4 160                                    Hydrated Clays                                                                B-80 (Thiele)   25   30    200-47                                                                             420                                                                              30-75                                                                             425                                                                              Condens.sup.a both cases            Barden-R (J. M. Huber)                                                                        25   30    170-42                                                                             405                                                                              45-35                                                                             230                                                                              Condens.sup.a undried               Champion Clay (Harwick)                                                                       25   30    160-37                                                                             440                                                                              16-26                                                                             215                                                                              Condens.sup.a undried               Hydrite UF (Georgia Kaolin)                                                                   25   30    102-39                                                                             390                                                                              0-6 160                                                                              Condens.sup.a undried               Oxides, Etc.                                                                  Aluminum oxide P (Degussa)                                                                    7.5  30    235-37                                                                             240                                                                              20-25                                                                             280                                                                              Condens.sup.a undried                                                         Fair Response                       Hydrated alumina                                                                              25   30    10-18                                                                              130                                                                               6-11                                                                             122                                    MAF Magnesium Oxide                                                                           25   30     4-11                                                                              110                                                                              3-8  85                                    Titanium oxide P-25 (Degussa)                                                                 10   30    30-25                                                                              200                                                                               3-10                                                                             175                                    Titanium oxide OR-450                                                                         25   30     8-15                                                                              145                                                                              3-7 205                                    (DuPont)                                                                      French Proc. ZnO Pasco 558                                                                    27   30    10-15                                                                              115                                                                              --  -- Not tested dried                    Lithopone       25   30    10-18                                                                              130                                                                               6-11                                                                             122                                    Hydrated lime   25   30    50-35                                                                              285                                                                               5-10                                                                             120                                                                              Condens.sup.a undried               Magnesium hydroxide                                                                           25   30    55-40                                                                              322                                                                              --  -- Decomposed when                                                               dried                               Diatomaceous Earth,                                                           Fullers Earth, Etc.                                                           Dicalite 103 (Gretco)                                                                         12.5 30    105-50                                                                             468                                                                              12-17                                                                             225                                                                              Condens.sup.a undried               Celite Silver Frost                                                                           12.5 30    50-40                                                                              325                                                                              14-17                                                                             175                                                                              Condens.sup.a undried               (Johns-Manville)                                                              Fullers Earth   25   30    165-73                                                                             500                                                                               5-10                                                                             160                                                                              Condens.sup.a undried               Felex 100, Feldspar                                                                           25   30    10-14                                                                              150                                                                              1-7 142                                    (Feldspar)                                                                    __________________________________________________________________________

                                      TABLE Ib                                    __________________________________________________________________________    Example I                                                                     Results of RF-Response of Various Inorganic Powders                           Moderate Response                                                                            Amount                                                                             Exposure,                                                                           Not dried                                                                             Dried                                       Material       Grams                                                                              Seconds                                                                             mA   °F.                                                                       mA   °F.                                                                       Observations                                                                           RF-Resp.                   __________________________________________________________________________    Treated Clays                                                                 Nucap 190, Mercaptosilane                                                                    25   30    305-60                                                                             560                                                                              20-62                                                                              375                                                                              Condens.sup.a                                                                          Mod. -d                    (J. M. Huber)                                                                 Nulok 390, Aminosilane                                                                       25   30    200-62                                                                             550                                                                              20-42                                                                              330                                                                              Condens.sup.a                                                                          Mod. -d                    (J. M. Huber)                                                                 Imvitone II Amine Bent. Clay                                                                 25   30    135-285                                                                            480                                                                               5-205                                                                             480                                                                              Condens.sup.a                                                                          Mod. +d                    (Ind. Min. Vent.)         5 sec.          Smoke evolution,                                                              charring                            __________________________________________________________________________

                                      TABLE Ic                                    __________________________________________________________________________    Example I                                                                     Results of RF-Response of Inorganic Powders                                   Good-Excellent Response                                                                      Amount                                                                              Exposure                                                                            Not Dried Dried                                    Material       Grams Seconds                                                                             mA    °F.                                                                        mA   °F.                                                                         Observations                                                                             RF-Resp.            __________________________________________________________________________    Oxides                                                                        Am. Proc. Zinc oxide, B                                                                      25    10    50-41 305 50-41                                                                              1100 GLOW.sup.b when                                                                          V. Good             (Smith C & C)                             (Est.)                              Amorphous Sodium Aluminum                                                     Silicates                                                                     Zeolex 7UD (J. M. Huber)                                                                     12.5  10    215-205                                                                             1100                                                                              20-195                                                                             1100 GLOW.sup.b in both                                                                       Exc.s                                                Est.     Est.                                Zeolex 23 (J. M. Huber)                                                                      10    10    175-175                                                                             1100                                                                              25-180                                                                             1100 GLOW.sup.b in both                                                                       Exc.s                                                Est.     Est.                                Zeolite Crystalline Sodium                                                    Aluminum Silicates                                                            Zeolite 4A, Detergent grade                                                                  12.5  35    265-255                                                                             1100                                                                              135-215                                                                            1100 Condens.sup.a in                                                                         Exc.                (Union Carb.)                    Est.                                                                              10 sec.                                                                            Est. cases. GLOW.sup.b in                                                          both cases                     Bentonite clays                                                               Nygel (Ind. Min. Ventures)                                                                   25    30    130-195                                                                             800 70-167                                                                             1100 Condens.sup.a                                                                            V. Good                                              Est.     Est. GLOW.sup.b when dried          Rheospan (Am. Colloid)                                                                       25    30    220-120                                                                             700 45-101                                                                              900 Condens.sup.a                                                                            Goodied                                              Est.     Est.                                HPM-20 (Am. Colloid)                                                                         25    30    150-120                                                                             575 65-110                                                                             1000 Slight condens.sup.a                                                                     Good                                                          Est. undried. Condens.sup.a                                                        undried.                       325 Mesh (H. M. Royal)                                                                       25    30    85-98 390 60-80                                                                               800 Flames, Charring                                                                         Good                                                          Est.                                __________________________________________________________________________     .sup.(a) Condensate observed on RF exposure                                   .sup.(b) Material glowed on RF exposure                                  

EXAMPLE II

Other tests were conducted with the same apparatus employed in Example Iin which amorphous sodium aluminum silicates (Table Ic, Example I) wereadmixed with several RF transparent polymers to provide polymercompositions with RF sensitivity. The results shown in Table II belowclearly demonstrate the effectiveness of the dried amorphous sodiumaluminum silicates in providing RF sensitivity to otherwise RFtransparent polymers.

                  TABLE II                                                        ______________________________________                                        Example II                                                                                          Sam- Expo- Cur-                                         Run           Wt. %   ple  sure, rent, Temp. Obser-                           No.  Polymer  Zeolex  wt, g                                                                              sec   mA    °F.                                                                          vation                           ______________________________________                                        1      A.sup.(a)                                                                            0       30   60    0-5   85    --                               2    A          5.sup.(e)                                                                           30   60    55-58 500   melted                           3      B.sup.(b)                                                                            0       12.5 30    0-5   85    --                               4    B          8.sup.(d)                                                                           12.5 30    35-40 580   melted                           5      C.sup.(c)                                                                            0       25   30    0-4   85    --                               6    C        .sup. 10.sup.(d)                                                                      25   60    35-38  600+ melted                           ______________________________________                                         .sup.(a) Polystyrene pellets.                                                 .sup.(b) Poly(phenylene sulfide) (PPS), Rytone ® powder type from         Phillips Petroleum Co. having a melt flow of 850 ± 100 g/10 min as         determined according to ASTM D 1238, Procedure B modified to use 5 kg         weight 600° F. (316° C.) and 0.17 mm orifice.                   .sup.(c) Poly(tetrafluoroethylene), Teflon ® polymer from E. I. duPon     Co. ground to a powder.                                                       .sup.(d) Zeolex 23 from J. M. Huber Corp.                                     .sup.(e) Zeolex 7 from J. M. Huber Corp.                                 

EXAMPLE III

Tests were conducted which examined the effect of added amorphous sodiumaluminum silicate on the microwave curing of a rubber compositioncontaining carbon black. The compounding recipe is shown below.

    ______________________________________                                        Recipe                                                                                          Parts, by wt                                                ______________________________________                                        Rubber.sup.(a)      100                                                       Oil and stabilizers 11.5                                                      Sulfur              0.5                                                       Zinc dimethyldithiocarbamate                                                                      3                                                         Zinc dibutyldithiocarbamate                                                                       3                                                         Carbon black, N-330 65                                                        Carbon black, N-550 30                                                        Calcium oxide in oil                                                                              10                                                        4,4'-Dithiodimorpholine                                                                           2                                                         Sodium Aluminum silicate.sup.(b)                                                                  0 or 9                                                    ______________________________________                                         .sup.(a) Oil extended (50 phr oil) ethylene/propylene/diene monomer (EPDM     rubber.                                                                       .sup.(b) Zeolex 23 from J. M. Huber Corp.                                

The compounds were mixed then fed in a continuous manner to a vacuumextruder and the extrudate fed to a microwave curing oven (10 KWDespatch oven made by Despatch Oven Co.) with surrounding air kept at500° F. to prevent heat loss then to a hot air oven with 500° F. hot airthen through a water bath for cooling before taken off on a turntable.At an extrudate cross section of about 0.4 square inch the results shownbelow were obtained.

    ______________________________________                                                          Run IIIa                                                                             Run IIIb                                                               (Control)                                                                            (Invention)                                          ______________________________________                                        Zeolex 23, phr      0        9                                                Linear speed, ft/min                                                                              20       27                                               Microwave power setting, KW                                                                       8        4                                                ______________________________________                                    

At an extrudate cross section of about 0.1 square inch the inventioncompound gave blistered product which indicated excessive temperatureduring curing which in turn indicated that 9 phr of the amorphous sodiumaluminum silicate was too much for the conditions used. However, theresults shown above for the thicker extrudate demonstrate a strongmicrowave cure promoting effect for the Zeolex 23 additive. This is seenby increased oven throughput and a reduced microwave power outputrequirement. It should also be noted that the cure promoting effect wasevident even though large amounts of carbon black were present in thecompound. Carbon blacks are known to promote microwave responsiveness inrubber compositions.

EXAMPLE IV

The RF responsiveness of both amorphous and crystalline sodium aluminumsilicates according to this invention was utilized to prepare sinteredpolymer compositions useful as filters and the like. These compositionsare especially useful when made from ultrahigh molecular weightpolyethylene (UHMWPE) because the resulting sintered polymercompositions have excellent strength properties even though they areporous.

In these tests the polymer powder (Hercules UHMWPE 1900 IV 22 or 27) andRF sensitizing additive were ballmilled for 45 minutes in a glass jarwith steel balls. The resulting mixture (about 18 g) was placed in theTeflon sample holder of the RF heating apparatus described in Example Iwhich served as the mold. In these runs the electrode platen distancewas 15/8 inch. Each mixture was subjected to very light mold pressure of5.5 g/cm² (none in Run 7 of Table IVa) during the RF radiationtreatment. The results obtained in these runs are presented in Table IVaand IVb below. The runs in Table IVa were made with an amorphous sodiumaluminum silicate, Zeolex 7 UD from J. M. Huber Corp. as the RFsensitizer while the runs in Table IVb were made with a crystallinesodium aluminum silicate, Arogen 3001 also from J. M. Huber Corp. as theRF sensitizer. Except as indicated for Runs 8 and 11-13 of Table IVb themold was exposed to RF radiation at ambient temperature, i.e. no moldpreheating.

                  TABLE IVa                                                       ______________________________________                                        Hercules UHMWPE 1900 IV 22                                                                                Cal-                                                           Ex-            culated                                                Sensi-  posure         %                                                 Run  tizer,  time,   Max-Min                                                                              Poros-                                            No.  php     sec     mA     ity.sup.(b)                                                                         Observations                                ______________________________________                                        1     5      240     35-35  --    Much loose powder                           2     5      330     40-35  --    Some loose powder,                                                            marginal.                                   3    10      120     60-40  49    Good, but some loose                                                          powder on surface.                          4    15      90      68-65  41    Very good. No loose                                                           powder.                                     5    20      90      70-65  42    Very good. No loose                                                           powder.                                     6    25      70      100-90 48    Fair. Loose powder                                                            on surface.                                 7.sup.(a)                                                                          20      90      68-62  43    Fair. Some loose                                                              powder on surface.                          ______________________________________                                         .sup.(a) No pressure applied to mold.                                         .sup.(b) Ratio of product specific gravity over polymer specific gravity      × 100.                                                             

                  TABLE IVb                                                       ______________________________________                                        Hercules UHMWPE 1900 IV 22.sup.(a)                                                                        Cal-                                                           Ex-            culated                                                Sensi-  posure         %                                                 Run  tizer,  time,   Max-Min                                                                              Poros-                                            No.  php     sec     mA     ity.sup.(b)                                                                         Observations                                ______________________________________                                         1    5      180     42-42  49    Good, but some loose                                                          powder on surface.                           2    5      240     43-43  47    Excellent                                    3   10      120     90-70  50    Excellent                                    4   15      90      112-105                                                                              52    Excellent                                    5   20      60      150-140                                                                              50    Very good                                    6   25      20      200-   50    Poor, much loose                                                              powder on surface                            7     10.sup.(b)                                                                          90      96-47  51    Excellent                                    8.sup.(c)                                                                           10.sup.(b)                                                                          60      100-50 54    Excellent                                    9.sup.(a)                                                                         10      120     90-72  51    Excellent                                   10.sup.(a)                                                                           10.sup.(d)                                                                          120     90-70  --    Poor, not sintered                          11.sup.(c)                                                                         15      60      135-125                                                                              50    Excellent                                   12.sup.(c)                                                                         15      30      135-125                                                                              49    Very good                                   13.sup.(c)                                                                           15.sup.(e)                                                                          45      137-72 51    Excellent                                   ______________________________________                                         .sup.(a) Runs 9 and 10 employed IV 27 type polymer.                           .sup.(b) Added 1 php of N--ethylo and ptoluene-sulfonamide.                   .sup.(c) Mold temperature increased to 320° F. before RF exposure.     .sup.(d) Added 1 php of glycerine.                                            .sup.(e) Added 2 php of an azodicarbonamide blowing agent (Porofor ADC/M      from Mobay Chemicals) and 0.5 php of American process type zinc oxide.   

The results in Tables IVa and IVb above show that sintered polymercompositions of suitable porosity and strength for use as filters can bereadily made from UHMWPE and amorphous or crystalline sodium aluminumsilicates employing RF heating. It was further shown that such filtermaterials have a very high absorption capacity for ordinary tobaccosmoke in that 20 mouthfuls of cigarette smoke blown through the samefilter area left only a small depth discolored.

It can also be seen that at about 25 php of inorganic RF sensitizerthere is interference with sintering of the UHMWPE polymer particles. Inthese tests about 10-15 php of sensitizer seemed to give best results.

Comparison of Runs 7 and 8 and Runs 4 and 11 of Table IVb show thatpreheating the mold to about 300°-350° F. can reduce RF exposure timeand improve surface sintering.

There is also indication that calculated porosity of the material can becontrolled by mold pressure, sensitizer level, exposure time and polymerparticle size. Porosity appears to reach a maximum just before polymerstarts to melt and mechanical strength also appears to peak near thissame point. This point is observed when the current just starts toincrease from a minimum after first having passed a maximum.

It is also seen that organic additives (Run 10 Table IVb), even in smallamounts, seem to interfere with the sintering though Runs 7 and 8 ofTable IVb show an exception to this effect.

It was also found that the RF sintering of polycarbonate orpoly(phenylene sulfide) polymer powders to form porous materials was notsuccessful because the samples melted. It is believed that the sharpmelting points of these polymers was responsible for this behavior.

EXAMPLE V

The effect of preheating conditions on the RF sensitivity of variousinorganic materials was examined. These tests were conducted in theapparatus previously described in Example I. These tests measured weight(moisture) loss as well as RF responsiveness of the inorganic materialafter the preheating treatment. The results are presented in Table Vbelow. In each test about 18 g of sample was employed for a 2 minutepreheat at the indicated temperature.

                  TABLE V                                                         ______________________________________                                        Run    Inorganic    Moisture                                                  No.    Material.sup.(a)                                                                           Loss, Wt %                                                ______________________________________                                                                      Time sec/to                                                                   Reach Temp °F.                            1     A            7.1       310/600°+                                 2     B            1.9       240/250°.sup.(b)                          3     C            9.6       150/Glow.sup.(b)                                 4     D            12.2       28/Glow.sup.(b)                                 5     E            13.9       70/Glow.sup.(b)                                 6     F            0          50/Glow.sup.(b)                                 7     G            11.        7/450°                                                                400° C. Preheat                           8     A            9.1       360/400°                                  9     B            31.8      240/400°                                 10     C            11.8      130/Glow.sup.(b)                                11     D            21.1       40/Glow.sup.(b)                                12     E            15.6       67/Glow.sup.(b)                                13     F            0          40/Glow.sup.(b)                                14     G            20.4       30/Glow.sup.(b)                                                              600° C. Preheat                          15     A            9.9       360/270°                                 16     B            --          --                                            17     C            16.8      500/Glow.sup.(b)                                18     D            22.2       40/Glow.sup.(b)                                19     E            16.3       58/Glow.sup.(b)                                20     F            0          30/Glow.sup.(b)                                21     G            21.8       60/Glow.sup.(b)                                ______________________________________                                         .sup.(a) A is a precipitated hydrated amorphous silica, Hi Sil 233.           B is a hydrated alumina, Hydral 705.                                          C is a Western bentonite clay, Nygel.                                         D is a crystalline sodium aluminum silicate (zeolite), Arogen 3001.           E is an amorphous sodium aluminum silicate, Zeolex 7 UD.                      F is an American process zinc oxide, Type B, lead free.                       G is a crystalline sodium aluminum silicate, Zeolite ZLD 1000.                .sup.(b) Material glowed on exposure to RF energy.                       

It is seen from Table V that RF responsiveness actually increased formaterials B, E and F after preheating at 200°, 400° and 600° C. whilematerial A decreased in RF responsiveness as the preheat temperatureincresed, apparently due to increasing moisture loss. Material C and Gfirst showed an increase in RF responsiveness on increasing preheattemperature from 200° to 400° C. but then decreased in RF responsivenessas the temperature was raised from 400° to 600° C. This decrease mayhave been due to a collapse of crystalline structure in these materialsat about 500° C. Material D appeared relatively insensitive to preheattemperature in terms of RF responsiveness even though significantmoisture loss occurred at each temperature which indicates that the RFresponsiveness of this material was not significantly dependent on itswater content.

EXAMPLE VI

Tests were conducted using the RF heating apparatus described in ExampleI at 1.5 inch electrode distance to examine the effect of polymerparticle size on RF responsiveness of polymer particles (20 g) admixed(ballmilled 30 minutes) with 5 php of crystalline sodium aluminumsilicate, Arogen 3001, Type 4A zeolite, particle size >1 micron, surfacearea >200 m² /g (BET/method) from J. M. Huber Corp. (The zeolite was notpreheated.) Exposure time in each run was 45 seconds and the recordedtemperature was obtained by use of a needle pyrometer. The resultsobtained in these runs are presented below in Table VI.

                  TABLE VI                                                        ______________________________________                                        Run                                                                           No.    Particle size (mesh)                                                                            Δ mAmp                                                                           °F.                                  ______________________________________                                        A. Poly(phenylene Sulfide).sup.(a)                                            1      >12               18-35    360                                         2      12 < 20           20-36    395                                         3      20 < 40           20-34    345                                         4      40 < 50           20-32    315                                         5      <50               19-29    283                                         6      Unfractionated    20-33    340                                         B. High MW HD Polyethylene.sup.(b)                                            7      >20               17-32    220                                         8      20 < 40           17-32    210                                         9      40 < 50           16-30    192                                         10     <50               16-30    189                                         11     Unfractionated    18-31    200                                         C. Ultrahigh MW Polyethylene.sup.(c)                                          12     >50               17-37    267                                         13     <50               18-36    264                                         ______________________________________                                         .sup.(a) Ryton ® MR03                                                     .sup.(b) Marlex ® HXM 50100                                               .sup.(c) Hercules 1900 IV 22                                             

As seen in Table VI above the larger polymer particles appear to be moreresponsive to RF heating. This may be due to a greater concentration ofRF sensitizer on the surface of said particles causing greater energyabsorption on the surface of the larger particles. If surfaceoverheating is expected to be very detrimental then it will bepreferable to use a smaller particle size for the polymer and with anarrow particle size distribution if possible. If coarser polymerparticles have to be used it would be preferable that they be mixed withsmaller polymer particles if possible.

EXAMPLE VII

Other tests were conducted with crystalline or amorphous sodium aluminumsilicates of various particle sizes used as RF sensitizers in ultrahighmolecular weight polyethylene (Hercules UHMWPE 1900, IV 22 powder). Allof the sodium aluminum silicates were supplied by J. M. Huber Corp. Thetests were made using the RF equipment previously described in ExampleI.

In each test 50 g of UHMWPE powder was ball milled for 30 min. with 2.5g of the sodium aluminum silicate. A 20 g portion of the blend wasplaced in the sample holder cavity taking care that the bed thicknesswas uniform. The lid was placed on top of the sample holder and thematerial exposed to RF cross-field at an electrode distance of 1.5 inchfor 30 and 60 seconds. As before, the temperature was measured with aneedle pyrometer. The ΔmAmp value is the difference between the actualmAmp reading with sample in place and the mAmp reading for RF exposureof the empty sample holder. The sample holder was cooled to roomtemperature before each test was run.

The results obtained in these tests are presented in Table VII below.

                                      TABLE VII                                   __________________________________________________________________________    Example VII                                                                                  BET         RF Exposure Time                                   Run                                                                              NaAl Ave. Particle                                                                        Surface                                                                             Wt. loss                                                                            30 sec. 60 sec.                                    No.                                                                              Silicate.sup.(a)                                                                   Size, microns                                                                        Area, m.sup.2 /g                                                                    %     Δ mAmp                                                                       °F.                                                                       Δ mAmp                                                                       °F.                            __________________________________________________________________________    1  A-1  5-7    180-225                                                                             6.sup.(b)                                                                           17-37                                                                              241                                                                              17-37                                                                              283                                   2  A-2  5-7    100-130                                                                             8.sup.(b)                                                                           11-31                                                                              213                                                                              11-31                                                                              273                                   3  A-3  5-7    60-80 3.5-5.5.sup.(b)                                                                      8-15                                                                              140                                                                               8-15                                                                              165                                   4  A-4  5-7    30-40 7.sup.(b)                                                                            5-12                                                                              121                                                                               5-12                                                                              139                                   5  A-5  7.6     23   15.4.sup.(c)                                                                        3-8  101                                                                              3-8  111                                   6  A-6  4.9     23   15.4.sup.(c)                                                                         3-13                                                                              109                                                                               3-13                                                                              119                                   7  C-7  3.7     3    20.4.sup.(c)                                                                         7-15                                                                              139                                                                               7-16                                                                              196                                   8  C-8   0.78  200   23.2.sup.(c)                                                                        15-39                                                                              243                                                                              14-36                                                                              270                                   9  C-9   0.91  200   23.4.sup.(c)                                                                        15-38                                                                              237                                                                              14-36                                                                              263                                   10  C-10                                                                              2.2    519   24.9.sup.(c)                                                                        12-17                                                                              163                                                                              11-16                                                                              217                                   11  C-11                                                                               0.99  415   26.7.sup.(c)                                                                        25-56                                                                              273                                                                              25-57                                                                              415                                   12  C-12                                                                               0.78  218   23.3.sup.(c)                                                                        15-41                                                                              250                                                                              15-40                                                                              278                                   13  C-13                                                                               0.83  274   23.5.sup.(c)                                                                        18-47                                                                              260                                                                              18-47                                                                              295                                   __________________________________________________________________________     .sup.(a) Samples designated A are amorphous while those showing C are         crystalline.                                                                  .sup.(b) Moisture loss.                                                       .sup.(c) Loss on ignition.                                               

The results shown in Table VII demonstrate that for the amorphous orcrystalline sodium aluminum silicates a significant improvement in RFsensitizing efficiency is seen in using those materials which have highsurface area and small particle size. It is also expected that the RFsensitizer materials of smaller particle size will have less effect onpolymer physical properties than similar materials of larger particlesize.

I claim:
 1. A method for molding wherein a substance suitable for radiofrequency enhancement is treated by the method comprising admixing withsaid substance suitable for radio frequency enhancement a radiofrequency sensitizing amount of zinc oxide (American process) inorganicradio frequency sensitizer treated essentially to remove absorbed an/orother volatiles and then subjected to radio frequency energy in amolding process.
 2. A method of claim 1 wherein said substance suitablefor enhancement of radio frequency sensitivity is a polymer.
 3. A methodof claim 2 wherein said polymer is ultra-high molecular weightpolyethylene.
 4. A method of claim 3 wherein said sensitizer has beenheat treated.
 5. A method of claim 4 wherein said sensitizer is presentin an amount in a range of about 1 weight percent to about 20 weightpercent based on total composition.
 6. A method for molding wherein asubstance suitable for radio frequency enhancement is treated by themethod comprising admixing with said substance suitable for radiofrequency enhancement a radio frequency sensitizing amount of bentoniteclay inorganic radio frequency sensitizer treated essentially to removeabsorbed water and/or other volatiles and then subjected to radiofrequency energy in a molding process.
 7. A method of claim 6 whereinsaid substance suitable for enhancement of radio frequency sensitivityis a polymer.
 8. A method of claim 7 wherein said polymer is ultra-highmolecular weight polyethylene.
 9. A method of claim 8 wherein saidsensitizer has been heat treated.
 10. A method of claim 9 wherein sidsensitizer is present in an amount in a range of about one weightpercent to about twenty weight percent based on total composition.
 11. Amethod of molding wherein a composition comprising a substance suitablefor enhancement of radio frequency sensitivity and a radio frequencysensitizing amount of zinc oxide (American process) inorganic radiofrequency sensitizer treated essentially to remove absorbed water and/orother volatiles is subjected to radio frequency energy in a moldingprocess.
 12. A method of claim 11 wherein said substance suitable forenhancement of radio frequency sensitivity is a polymer.
 13. A method ofclaim 12 wherein said polymer is ultra-high molecular weightpolyethylene.
 14. A method of claim 13 wherein said sensitizer has beenheat treated.
 15. A method of claim 14 wherein said sensitizer isadmixed in an amount in a range of about 1 weight percent to about 20weight percent based on total composition.
 16. A method for moldingwherein a composition comprising a substance suitable for enhancement ofradio frequency sensitivity and a radio frequency sensitizing amount ofbentonite clay inorganic radio frequency sensitizer treated essentiallyto remove absorbed water and/or other volatiles is subjected to radiofrequency energy in a molding process.
 17. A method of claim 16 whereinsaid substance suitable for enhancement of radio frequency sensitivityis a polymer.
 18. A method of claim 17 wherein said polymer isultra-high molecular weight polyethylene.
 19. A mmethod of claim 18wherein said sensitizer has been heat treated.
 20. A method of claim 19wherein said sensitizer is admixed in an amount in a range of about 1weight percent to about 20 weight percent based on total composition.